Interpersonal timing is a critical capacity in the development of normal communication. We have available an automated system that times the sequence of vocal sounds and silences in an interaction and uses a statistical procedure (time-series regression analysis) to assess the magnitude of influence exerted by each participant's timing on the other's. Using this method: (a) Mutual influence has been demonstrated for the conversations of normal adults; (b) A series of 3 cross-sectional pilot studies of affective and vocal behaviors in 40 infants shows that normal mothers and infants also influence the temporal patterns of each other's behavior; and (c) Defective timing has been demonstrated in adult psychopathological communication. We now propose to use this method to quantify interpersonal timing in adult-infant dyads in the course of development prior to speech onset. Since our method can detect interpersonal timing deficits in adult psychopathology, it can potentially do the same in disturbed mother-infant pairs. But first we must specify the normal Developmental course of this critical stage. The research design is a longitudinal study of 100 full term normal infants at one, four and twelve months. Infants are audiotaped while interacting with their mothers and with a stranger. The "stranger" design permits assignment of responsibility for influence to the mother, the infant, or both. Measures of prelinguistic timing will be related to pre-, peri-, and postnatal factors, to other conventional social measures at each age, and to conventional outcome measures of social and cognitive development at one year. The norms developed in this study will contribute to our ultimate goal; an objective, automated behavioral test for the detection of soical deficits in the first year of life.